Optical disc devices read and write data from and into one or more media, such as a digital versatile disc (DVD) or a Blu-ray (registered trademark) disc (BD).
Optical disc devices, for example, include a spindle motor, a spindle motor drive unit, an optical pick-up unit (OPU), and a control unit. The spindle motor and spindle motor drive unit control the rotation of an optical disc. The optical pick-up unit reads data stored in the optical disc. The control unit provides control over components of the optical disc device.
An optical pickup, for example, includes an objective lens and a receiver unit. The objective lens focuses a laser light from a predetermined light source anywhere on an optical disc. The receiver unit receives light reflected off the optical disc.
It should be noted that optical disc devices in general perform tracking control for an optical pickup by a differential push-pull method. Alternatives for the tracking control for optical pickup include a phase contrast method.
In the differential push-pull method, the optical pickup generates one main beam and two sub beams from light output from a light source and emits the beams to an optical disc. The receiver unit of the optical pickup receives light of the main beam reflected off the optical disc to generate a main push-pull signal. The receiver unit also receives light of the sub beams reflected off the optical disc to generate a sub push-pull signal. The signal processing unit of the optical disc device subtracts a signal obtained by multiplying the sub push-pull signal K times from the main push-pull signal to generate a differential push-pull signal. The signal processing unit generates a tracking-error signal from the generated differential push-pull signal.